Fuel injection systems inject fuel for combustion in internal combustion engines. In particular for late cylinder direct injection compression ignition engines, such as conventional diesel engines, it has been found that various aspects of the fuel injection event can have a significant impact on the extent of harmful emissions produced in combustion. Some of these factors include the quantity of fuel injected, the number of fuel injection events per cycle, the respective timing of such injection event(s), the fuel injection pressure, rate shaping of the injection event, the various geometries and spacings between the fuel injector and combustion bowl, and the fuel injector nozzle geometry (including number, size, and orientation of holes in the injector nozzle, etc. . . . ).
In order to reduce formation of the harmful pollutant NOx in combustion, many experts advocate avoidance of unnecessary increases in the surface area of fuel exposed to oxygen in the initial portion of a fuel injection event. This generally means limiting the number of holes used in the fuel injector nozzle. As a recent example, U.S. Pat. No. 6,966,294 to Eckerle teaches away from the use of more than six holes in a fuel injector nozzle for a diesel engine, for the stated reason that the use of a greater number of nozzle holes would result in a harmful increase in the formation of NOx in combustion.
In commonly assigned U.S. Pat. No. 6,857,263, which is incorporated herein by reference, applicant set forth a low emission diesel combustion system that reduces NOx formation in combustion, in part through the use of low oxygen concentrations in combustion. With dilute combustion such as this (e.g., with the oxygen concentration of the charge-air used for the main combustion event preferably between 10% and 15%, and more preferably between 12% and 14%), applicant has found it desirable, in contrast, to create greater mixing and greater fuel contact with oxygen as fuel comes out of the fuel injector into the combustion chamber.
U.S. Pat. No. 6,820,587 to Hoglund (column 7, line 65, et seq.) teaches the possibility of a fuel injector nozzle having double rows of openings.